1. Field of the Invention
The present invention relates to a method for sharing a backup path in a MultiProtocol Label Switching (MPLS) network, a label switching router (LSR) for setting a backup path in an MPLS network a system for setting a backup path in an MPLS network, and a recording medium therefor.
2. Description of the Related Art
In order to completely recover a failure occurring in a link on a working path satisfying band conditions typically given in an MPLS network, it is necessary to disjoint the working path and joint another path referred to as a backup path satisfying the band conditions of the working path.
The conception of an MPLS network in which a backup path is not shared will be described with reference to FIG. 1.
A label switched path (LSP) L1 103 denoting a working path (represented by a solid line) between a source LSR1 101 and a destination LSR12 102 is set via LSR3-LSR6-LSR8, and a backup path (represented by a dotted line), LSP L1b 104, which is disjointed from the L1 is set as LSR1-LSR4-LSR5-LSR9-LSR10-LSR12. In addition, a working path LSP L2 106 is set between a source LSR2 105 and a destination LSR12 102 via LSR7-LSR11, and a backup path LSP L2b 107 disjointed from the L2 is set as LSR2-LSR5-LSR9-LSR10-LSR12.
Here, the L1b and the L2b pass through the same links while passing a path LSR5-LSR9-LSR10-LSR12. However, since conception of band sharing between backup paths is not defined, bands for both backup paths should be guaranteed, respectively, at each of the links. When it is assumed that only single link failure occurs at one time in a single network, the backup paths L1b and L2b are not simultaneously used since a failure does not occur in the L1 and L2 at the same time. Nevertheless, bands for both backup paths L1b and L2b are maintained, wasting network resources.
The above-described single link failure is based on the following facts Generally, a backup path is set to a less optimal path than a working path and is temporarily used until the working path is restored, so the backup path is used for a short period of time. A probability of failures occurring in a plurality of links for that short period of time is very low. In addition, maintaining a plurality of backup paths to restore a plurality of link failures occurring simultaneously results in significant waste of network resources, so it is reasonable to consider only a single link failure to be recovered without considering a plurality of link failures.
It is also waste of resources to set backup paths for every working path to recover a temporary failure. To compensate for this waste, it is necessary for the backup paths of working paths passing through different links to share a band. In other words, when a single link failure occurs in a single network, discontinuation of a service occurs only a single working path. In this circumstances, a working path having a failure can be completely restored even if the backup path of the working path shares a band with the backup paths of other working paths.
The conception of an MPLS network in which a backup path is shared will be described with reference to FIG. 2.
Link configuration of each path shown in FIG. 2 is the same as in FIG. 1. However, a bandwidth allocated to links through which working paths L1b and L2b pass in a section LSR5-LSR9-LSR10-LSR12 greatly decreases as compared to the case of FIG. 1. In other words, generally, failures do not simultaneously occur in both working paths L1 and L2, so a band allocated to the same link through which the backup paths L1b and L2b of the respective working paths L1 and L2 pass is set to a maximum, MAX(L1b, L2b) 201, between bands required by the two backup paths L1b and L2b. Accordingly, even if a failure occurs in the working path L1 or L2, the corresponding backup path L1b or L2b has an enough band to recover the working path L1 or L2.
However, backup paths can share a band only when the corresponding working paths are disjointed from each other. In other words, when a failure occurs in one link, the backup paths of all working paths passing through the link must not share a band, and the sum of bandwidths of the working paths must be guaranteed for a backup path. In order to guarantee a backup path in such circumstances, information about link configurations of all paths set currently must be reported to all nodes and managed continuously.
In other words, all nodes must recognize and manage information about configurations of all working paths and backup paths which are previously set, that is, link information of each of the paths, bandwidth information allocated to the working paths, and bandwidth information allocated to the backup paths. The quantity of information that must be maintained and managed is so enormous that traffic for reporting the information to all of the nodes causes a network service to fail. In addition, each of the node is burdened with a large quantity of loads. Accordingly, it is impossible to exactly allow backup paths to share a band in conventional researches.